Query Args

functions.php

<?php
function themeslug_query_vars( $qvars ) {
  $vars[] = 'headertype';
  return $vars;
}
add_filter( 'query_vars', 'themeslug_query_vars' , 10, 1 );

header.php

<?php
$headernumb = get_query_var( 'headertype' );

// Kalo query_var ada, jadi prioritas
if( $headernumb ){
  $headertype = $headernumb;
  
// Kalo query_var di browser url address gak ada, tarik dari theme option
} else {
  $headertype = my_option('headertype', 3);
}

// tarik file: header-n.php
get_template_part('header', '$headertype');